KR20040082043A - Orthogonal Frequency Division Multiplexor transceiving unit of wireless Local Area Network system providing for symbol timing synchronization by double correlation and double peak comparison and symbol timing synchronization method thereof - Google Patents

Abstract

PURPOSE: An OFDM receiver of a wireless LAN system for performing a symbol timing synchronization process by comparing a repetitive correlation value with a second peak value and a symbol synchronization method thereof are provided to improve a correlation characteristic by performing the first and the second peak value comparison processes. CONSTITUTION: An RF module(210) receives a wireless signal and extracts an OFDM analog signal from an assigned channel. An A/D converter(220) converts the OFDM analog signal to a digital signal. A first differential cross correlator(230) outputs the first differential cross correlation value. A second differential cross correlator(240) outputs the second differential cross correlation value. A first peak detector(250) outputs the first interface detection information corresponding to the first condition by comparing the first peak values each other. A second peak detector(260) outputs the second interface detection information corresponding to the second condition by comparing the second peak values each other. A symbol clock generator(270) generates a symbol clock synchronized with the first peak position. An IFFT(280) synchronizes the digital signal with the symbol clock and outputs the digital signal.

Description

Orthogonal Frequency Division Multiplexor transceiving unit of wireless Local Area Network system providing for symbol timing synchronization by double correlation and double peak comparison and symbol timing synchronization method

The present invention relates to a wireless local area network (hereinafter, abbreviated as "LAN"), and more particularly to orthogonal frequency division multiplexing, i.e., orthogonal frequency division multiplexor (OFDM) receivers and methods of a wireless LAN system. It is about.

A wireless LAN system wirelessly connects a local area network (LAN) of a private or public network, providing convenience to users who use devices such as computers, mobile communication terminals, and the like in transmitting and receiving information. In particular, OFDM signals using a high frequency band are generally transmitted and received at a transmission rate of up to 54 Mbps via multiple carriers in the 5.4 GHz band, as defined in IEEE 802.11.a. In addition, in IEEE 802.11, various types of signal systems, such as a direct sequence spread spectrum (DSSS) signal and a complementary code keying (CCK) signal, are defined. Here, an OFDM receiver for receiving an OFDM signal is described.

FIG. 1 is a diagram illustrating a general OFDM signal specification detailing a preamble section. Referring to FIG. 1, the preamble standard defined in IEEE802.11a is shown in detail. That is, the preamble section of the OFDM signal includes a short training symbol section having 10 repetition patterns for at least 8 ms and one guard interval (GI) and two repetition patterns for the next 8 ms. The branch is composed of a long training symbol section. In the short training symbol section, the signal is 16 samples long, and in the long training symbol section, the signal is 64 samples long. In this case, the symbol timing synchronization method is a method of finding a boundary between a short training symbol interval and a long training symbol interval.

A method of generating a symbol clock by performing cross correlation and peak detection using a short training symbol or a long training symbol as a reference signal to find a boundary between a short training symbol interval and a long training symbol interval. In the conventional symbol time synchronization method, since a method using a training symbol with a long training symbol as a reference signal exhibits better cross-correlation property, a cross correlation is generally performed using a long training symbol as a reference signal. . However, since the long training symbol interval is received later than the short training symbol in time, such a method causes the response speed of the entire system to be slowed down. More specific operation of signal reception processing in an OFDM receiver is well described in the European patent, EP1,126,673.

However, in the conventional symbol time synchronization method as described above, the method of performing cross-correlation using a long training symbol as a reference signal has a long correlation execution time while passing a correlator during a long training symbol interval, thereby improving correlation characteristics. Although there is an advantage, it is impossible to estimate the fine frequency offset and estimate the channel coefficient in the equalizer until the symbol synchronization is performed. Therefore, such a method causes a problem of slowing down the response speed of the system, and adding another technique for overcoming this increases the complexity of the system.

On the other hand, in the conventional symbol time synchronization method as described above, a method of performing cross-correlation using a short training symbol as a reference signal increases the response speed of the system. However, in this method, since the AGC (Auto Gain Control) is performed from the initial t1 to t7 among the short training symbol intervals of FIG. 1 due to the characteristics of the IEEE802.11a receiver, only three pattern sections from t8 to t10 are performed. There is a problem in that it is used as a valid time to degrade the correlation characteristics. In addition, since the number of signal samples of the short training symbol is small, there is a problem in that the correlation characteristics are deteriorated due to the influence of noise, frequency offset, etc. more than the long training symbol.

Accordingly, the technical problem to be achieved by the present invention is to perform a first order differential cross correlation robust to a frequency offset by using the differential value of the short training symbol as a reference signal, Based on the auto correlation value of the difference value (auto correlation value) based on the output value of the first differential cross correlation is again correlated, and the peak value of the second correlation with respect to the output value of the correlation again In addition, the present invention provides an OFDM receiver of a wireless LAN system capable of improving the response speed of a system by improving correlation characteristics and enabling symbol synchronization within a short time.

Another technical problem to be solved by the present invention is to perform a first order differential cross correlation that is robust to a frequency offset using the difference value of a short training symbol as a reference signal, and based on the autocorrelation value of the difference value of the short training symbol. Corresponding to the output value of the first-order differential cross-correlation, and through the second-order rough peak comparison with respect to the output value of the correlation, the correlation characteristics are improved and the symbol synchronization can be performed quickly. It is to provide an OFDM reception method of a wireless LAN system that can increase the speed.

BRIEF DESCRIPTION OF THE DRAWINGS In order to better understand the drawings cited in the detailed description of the invention, a brief description of each drawing is provided.

FIG. 1 is a diagram illustrating a general OFDM signal specification detailing a preamble section.

2 is a block diagram of an OFDM receiver of a wireless LAN system according to an embodiment of the present invention.

3 is a flowchart illustrating an operation of an OFDM receiver of FIG. 2.

4 is a simulation result of the output waveform of the first order cross correlation unit of FIG. 2.

5 is an example of waveforms for differential values of short training symbols.

FIG. 6 is a graph illustrating autocorrelation values for the waveform of FIG. 5.

7 is a graph illustrating synchronization probability when a long training symbol is used as a reference value of a cross correlation unit in a general OFDM receiver.

FIG. 8 is a graph illustrating synchronization probabilities of the OFDM receiver of FIG. 2.

OFDM receiver of a wireless LAN system according to the present invention for achieving the above technical problem, the RF module unit, AD conversion unit, the first differential cross correlation unit, the second differential cross correlation unit, the first peak detection unit, the second peak A detector, a symbol clock generator, and an IFFT unit are provided.

The RF module unit receives the wireless airwaves and extracts and outputs an OFDM analog signal from a signal present in the assigned channel.

The AD converter samples the OFDM analog signal, converts it into a digital signal, and outputs the digital signal.

The first differential cross correlation unit outputs a predetermined first differential cross correlation value Z1 as a predetermined cross correlation between the digital signal and the difference value DVTS of the short training symbol of the OFDM standard.

The second differential cross correlation unit is a second differential cross correlation value Z as the cross correlation between the predetermined first differential cross correlation value Z1 and the autocorrelation value ACVTS of the difference value DVTS of the short training symbol. )

The first peak detector is a first peak, which is the highest peak among the first or previous 16 sampling values of the second differential cross correlation value Z, in response to the second boundary detection information when the initial or predetermined second condition is satisfied. To detect the primary boundary corresponding to the first predetermined condition by comparing the value Z (dmax * (i-1)) with the first peak Z (dmax * (i)), which is the highest peak among 16 sampling values from the next position. Information P1 is output.

The second peak detector is next to the highest peak value among the previous 16 sampling values of the second differential cross correlation value Z in response to the first boundary detection information P1 when the first predetermined condition is satisfied. The second peak value Z (dmax + 1 * (i-1)), which is the sampling value, and the second peak value Z (dmax + 1 * (i)), which is the next sampling value after the highest peak among the 16 sampling values from the next position; In comparison, the secondary boundary detection information P corresponding to the predetermined second condition is output.

The symbol clock generation unit activates the primary boundary detection information P1 when the predetermined first condition is not satisfied, or the secondary boundary detection information P when the predetermined second condition is not satisfied. Accordingly, the symbol clock SCLK, which is a clock synchronized with the position dmax (i-1), is regarded as the boundary between the short training symbol section and the long training symbol section according to the OFDM standard according to the first peak position dmax (i-1). To generate the output.

The IFFT unit outputs a digital symbol IFTS processed by IFFT by synchronizing the digital signal with the symbol clock SCLK.

The predetermined cross correlation is represented by a formula representing the digital signal,

Where P _k is the k th sample signal, b _k is the ideal k th sample signal in the time domain, T _s is the sample interval, θ ₀ is the initial phase value, N is the point size of the IFFT, and a _n is the nth subchannel. Data symbol on the sender side)

And an equation representing a difference value DVTS of the short training symbol.

Where R1 (k) is the difference between short training symbols

By,

Where d is the location of the time domain

Is calculated to represent the predetermined first-order differential cross correlation value Z1,

(Where Z1 (d) is the first-order differential cross correlation value)

It is characterized by calculating the.

The predetermined first condition is expressed by equation,

β * Z (dmax * (i-1)) <Z (dmax * (i))

(Where β is an arbitrary coefficient, Z (dmax * (i-1)) is the initial or previous primary peak, dmax * (i-1) is the position of the initial or previous primary peak, Z (dmax * ( i)) is the current primary peak and dmax * (i) is the current primary peak)

And β is 0.5 or less.

The primary boundary detection information P1 is deactivated when the predetermined first condition is satisfied, and is activated when the predetermined first condition is not satisfied.

The predetermined second condition is expressed by equation,

γ * Z (dmax + 1 * (i-1)) <Z (dmax + 1 * (i))

Where γ is any coefficient, Z (dmax + 1 * (i-1)) is the initial or previous secondary peak, dmax * (i-1) is the position of the initial or previous secondary peak, Z (dmax * (i)) is the current secondary peak, dmax * (i) is the current secondary peak)

(Gamma) is characterized by being 0.35 or less.

The secondary boundary detection information P is deactivated when the predetermined second condition is satisfied, and is activated when the predetermined second condition is not satisfied.

The OFDM reception method of a wireless LAN system according to the present invention for achieving the above another technical problem, comprises the following steps.

That is, in the OFDM reception method of the wireless LAN system according to the present invention, the wireless LAN system first receives wireless airwaves and extracts and outputs an OFDM analog signal from a signal present in an allocated channel. Next, the WLAN system samples the OFDM analog signal, converts the OFDM analog signal into a digital signal, and outputs the digital signal. The wireless LAN system generates a first-order difference with a predetermined cross correlation between the digital signal and a short training symbol of the OFDM standard. Outputs a cross correlation value (Z1) and quadratic differential cross correlation as the cross correlation of the predetermined first differential cross correlation value (Z1) and the autocorrelation value (ACVTS) of the difference value (DVTS) of the short training symbol; Output the value (Z). Subsequently, the WLAN system, in response to the secondary boundary detection information P when the initial or predetermined second condition is satisfied, is the highest among the initial or previous 16 sampling values of the second differential cross correlation value Z. The peak first peak Z (dmax * (i-1)) is compared with the first peak peak Z (dmax * (i)), which is the highest peak of 16 sampling values from the next position, to correspond to the first predetermined condition. Outputs the first boundary detection information P1, and in response to the first boundary detection information P1 when the first predetermined condition is satisfied, the previous 16 samplings of the second differential cross correlation value Z are performed. The second peak value Z (dmax + 1 * (i-1)), the highest peak next sampling value among the values, and the second peak peak Z (dmax +, the next sampling value among the 16 sampling values from the next position. Compared with 1 * (i), the secondary boundary detection information P corresponding to the second predetermined condition is output. Accordingly, the wireless LAN system is configured to perform the first boundary detection information P1 when the predetermined first condition is not satisfied, or the second boundary detection information P when the predetermined second condition is not satisfied. ) Is activated, the primary peak position dmax (i-1) is a clock synchronized with the position dmax (i-1) as a boundary between the short training symbol interval and the long training symbol interval in the OFDM standard. A symbol clock (SCLK) is generated and output, and the digital signal (IFTS) subjected to IFFT processing is output by synchronizing the digital signal with the symbol clock (SCLK).

The predetermined cross correlation is represented by a formula representing the digital signal,

Where P _k is the k th sample signal, b _k is the ideal k th sample signal in the time domain, T _s is the sample interval, θ ₀ is the initial phase value, N is the point size of the IFFT, and a _n is the nth subchannel. Data symbol on the sender side)

And an equation representing a difference value DVTS of the short training symbol.

Where R1 (k) is the difference between short training symbols

By,

Where d is the location of the time domain

Is calculated to represent the predetermined first-order differential cross correlation value Z1,

(Where Z1 (d) is the first-order differential cross correlation value)

It is characterized by calculating the.

The predetermined first condition is expressed by equation,

β * Z (dmax * (i-1)) <Z (dmax * (i))

(Where β is an arbitrary coefficient, Z (dmax * (i-1)) is the initial or previous primary peak, dmax * (i-1) is the position of the initial or previous primary peak, Z (dmax * ( i)) is the current primary peak and dmax * (i) is the current primary peak)

And β is 0.5 or less.

The primary boundary detection information P1 is deactivated when the predetermined first condition is satisfied, and is activated when the predetermined first condition is not satisfied.

The predetermined second condition is expressed by equation,

γ * Z (dmax + 1 * (i-1)) <Z (dmax + 1 * (i))

Where γ is any coefficient, Z (dmax + 1 * (i-1)) is the initial or previous secondary peak, dmax * (i-1) is the position of the initial or previous secondary peak, Z (dmax * (i)) is the current secondary peak, dmax * (i) is the current secondary peak)

(Gamma) is characterized by being 0.35 or less.

The secondary boundary detection information P is deactivated when the predetermined second condition is satisfied, and is activated when the predetermined second condition is not satisfied.

In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings which illustrate preferred embodiments of the present invention and the contents described in the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements.

2 is a block diagram of an OFDM receiver of a wireless LAN system according to an embodiment of the present invention.

2, the OFDM receiver of the wireless LAN system according to an embodiment of the present invention, the RF module unit 210, AD converter 220, the first difference cross correlation unit 230, the second difference intersection A correlator 240, a primary peak detector 250, a secondary peak detector 260, a symbol clock generator 270, and an IFFT unit 280 are provided.

The RF module unit 210 receives the wireless airwaves and extracts and outputs an OFDM analog signal from a signal existing in the assigned channel. In general, OFDM wireless transmission signals are transmitted and received at up to 54 Mbps transmission rates over multiple subchannels in the 5.4 GHz band, as defined in IEEE802.11a.

The AD converter 220 samples the OFDM analog signal and converts the OFDM analog signal into a digital signal. The first differential cross correlation unit 230 outputs a predetermined first differential cross correlation value Z1 as a predetermined cross correlation between the digital signal and the difference value DVTS of the short training symbol of the OFDM standard. The second differential cross correlation unit 240 crosses a second differential with the first correlation cross correlation value Z1 and the cross correlation of the autocorrelation value ACVTS of the difference value DVTS of the short training symbol. Output the correlation value Z.

Here, the predetermined cross correlation is calculated by using Equation 1 representing the digital signal and Equation 2 representing the difference value DVTS of the short training symbol. [Equation 4] representing the first-order differential cross correlation value Z1 is calculated. For a cross correlation method that considers the phase difference of two adjacent sample signals with the difference of short training symbols (DVTS) in order to show the robust correlation characteristics in the frequency offset of the received signal, H. Kobayashi's paper, [ "A Novel Symbol Frame and Carrier Frequency Synchronization for Burst Mode OFDM Signal" Proceedings of VTC 2000 Fall.

Where P _k is the k th sample signal, b _k is the ideal k th sample signal in the time domain, T _s is the sample interval, θ ₀ is the initial phase value, N is the point size of the IFFT, and a _n is the nth subchannel. Data symbol on the sender side)

Where R1 (k) is the difference between short training symbols

Where d is the location of the time domain

(Where Z1 (d) is the first-order differential cross correlation value)

In response to the second boundary detection information P when the initial or predetermined second condition is satisfied, the first peak detection unit 250 includes one of the first or previous 16 sampling values of the second differential cross correlation value Z. The first peak, Z (dmax * (i-1)), which is the highest peak, is compared to the first peak, Z (dmax * (i)), which is the highest peak of 16 sampling values from the next position. The corresponding primary boundary detection information P1 is output. The second peak detector 260 is the highest of the previous 16 sampling values of the second differential cross correlation value Z in response to the first boundary detection information P1 when the first predetermined condition is satisfied. The second peak value Z (dmax + 1 * (i-1)), which is the next peak value, and the second peak value Z (dmax + 1 * (i), the next peak value of the 16 sampling values from the next position. Compared with)), the secondary boundary detection information P corresponding to the second predetermined condition is output.

The predetermined first condition corresponds to Equation 5, β is 0.5 or less, and the primary boundary detection information P1 is deactivated when the predetermined first condition is satisfied, that is, the first logical state ( Logic low state), and if the predetermined first condition is not satisfied, the second logic state is activated from the first logic state to the second logic state (logical high state).

β * Z (dmax * (i-1)) <Z (dmax * (i))

(Where β is an arbitrary coefficient, Z (dmax * (i-1)) is the initial or previous primary peak, dmax * (i-1) is the position of the initial or previous primary peak, Z (dmax * ( i)) is the current primary peak and dmax * (i) is the current primary peak)

The predetermined second condition corresponds to Equation 6, and γ is 0.35 or less, and the secondary boundary detection information P is deactivated when the predetermined second condition is satisfied, that is, the first logical state ( Logic low state), and if the predetermined second condition is not satisfied, the second logic state is activated from the first logic state to the second logic state (logical high state).

γ * Z (dmax + 1 * (i-1)) <Z (dmax + 1 * (i))

Where γ is any coefficient, Z (dmax + 1 * (i-1)) is the initial or previous secondary peak, dmax * (i-1) is the position of the initial or previous secondary peak, Z (dmax * (i)) is the current secondary peak, dmax * (i) is the current secondary peak)

The symbol clock generation unit 270 performs the first boundary detection information P1 when the predetermined first condition is not satisfied, or the second boundary detection information P when the predetermined second condition is not satisfied. ) Is activated, the primary peak position dmax (i-1) is a clock synchronized with the position dmax (i-1) as a boundary between the short training symbol interval and the long training symbol interval in the OFDM standard. Generate and output a symbol clock (SCLK). The IFFT unit 280 outputs a digital symbol IFTS processed by IFFT by synchronizing the digital signal with the symbol clock SCLK.

Hereinafter, the operation of the OFDM receiver of the wireless LAN system according to an embodiment of the present invention will be described in more detail.

3 is a flowchart illustrating an operation of an OFDM receiver of FIG. 2.

Referring to FIG. 3, an OFDM receiver according to an embodiment of the present invention first receives radio airwaves and extracts and outputs an OFDM analog signal from a signal existing in an allocated channel by the RF module unit 210. (S310). Next, the AD converter 220 samples the OFDM analog signal and converts the OFDM analog signal into a digital signal (S320). The first-order differential cross correlation unit 230 is a short training symbol of the digital signal and the OFDM standard. The first differential cross correlation value Z1 (d) as shown in [Equation 4] is output as a predetermined cross correlation with respect to the difference value DVTS of S33 to S340. The second differential cross correlation unit 240 crosses a second differential with the first correlation cross correlation value Z1 and the cross correlation of the autocorrelation value ACVTS of the difference value DVTS of the short training symbol. The correlation value Z (d) is output (S350 to S360). Here, the second differential cross correlation value Z (d) is calculated based on the autocorrelation value ACVTS of the predetermined first differential cross correlation value Z1 and the difference value DVTS of the short training symbol. As in the differential differential cross correlation unit 230, cross correlations such as Equations 1 to 4 are performed once more.

4 is a simulation result of the output waveform of the first order cross correlation unit of FIG. 2.

Referring to FIG. 4, the output waveforms of the first-order cross correlation unit of FIG. 2 show ten peaks in t1 to t10 sections (7e-6 to 15e-6 sections in FIG. 4) which are short training sections. The waveform of FIG. 4 is a simulation result when the SNR is 5dB and the normalized frequency offset is 1.235 in the QPSK modulation scheme of the multipath fading channel environment. As described above, ten peaks appear in the simulation, but since the intervals t1 to t7 substantially perform AGC and the like, the peaks effective for the first-order differential cross correlation unit 230 are short, as shown in FIG. 4. There are only three peaks that appear before the end of the training symbol interval. As shown in FIG. 4, even when the frequency offset is 1.235, the frequency offset is robust.

In the low SNR or multipath fading channel environment, there are many distortions in the peak value in the 16 sample intervals of the short training symbol. For this reason, in the conventional symbol synchronization method, it is difficult to accurately determine the peak position, and the performance of symbol synchronization is not good. In order to solve this problem, the present invention performs the correlation again by setting the autocorrelation value ACVTS of the difference value DVTS of the short training symbol to the reference signal value of the second order cross correlation unit.

5 is an example of a waveform for the difference value DVTS of a short training symbol.

Referring to FIG. 5, a waveform of a difference value (DVTS) of short training symbols of the OFDM standard defined in IEEE802.11a is shown.

FIG. 6 is a graph illustrating the autocorrelation value ACVTS for the waveform of FIG. 5.

Referring to FIG. 6, a graph of the autocorrelation value (ACVTS) of the waveform itself of FIG. 5 is shown, which is used as data for determining the characteristics of the correlation. As shown in FIG. 6, the values on the left and right sides of the peak value are about 80% of the peak value and the next left and right values are about 50%, which is not a good correlation characteristic. That is, it means that the position of the peak value determined by the receiver due to the noise is likely to be mistaken as the position indicating the left or right side of the peak value of FIG. 6. In order to solve this problem, in the present invention, the first peak detection unit 250 and the second peak detection unit 260 are provided to perform the peak comparison over the second order.

On the other hand, the first peak detection unit 250 initially, the first peak of the highest peak among the first 16 sampling values of the second differential cross correlation value (Z) Z (dmax * (i-1)) and its position dmax * (i-1), the second peak value Z (dmax + 1 * (i-1)), which is a sampling value after the highest peak value, and the position dmax + 1 * (i-1) are searched for (S370).

Accordingly, the first peak detector 250 initially obtains the first peak value Z (dmax * (i-1)), which is the highest peak value among the 16 sampling values of the second differential cross correlation value Z, Primary boundary detection information P1 corresponding to the first predetermined condition S380 of [Equation 5], compared with the primary peak Z (dmax * (i)), which is the highest peak among 16 sampling values from the position. Outputs (S390). In addition, the first peak detector 250 transfers the second differential cross correlation value Z in response to the second boundary detection information P when the predetermined second condition is satisfied (S400 to S410). Compare the primary peak Z (dmax * (i-1)), which is the highest peak of the 16 sampling values, with the primary peak Z (dmax * (i)), which is the highest peak of the 16 sampling values from the next position, Primary boundary detection information P1 corresponding to the first predetermined condition S380 of Equation 5 is output (S390).

The second peak detector 260 transfers the second differential cross correlation value Z in response to the first boundary detection information P1 when the predetermined first condition of Equation 5 is satisfied. The second peak value Z (dmax + 1 * (i-1)), which is the next peak value of the 16 sampling values, is the second peak peak Z (, which is the next peak value of the 16 sampling values from the next position. Compared to dmax + 1 * (i), the second boundary detection information P corresponding to the predetermined second condition S400 of Equation 6 is output (S390).

In Equation 5, the β is preferably about 0.5, and the primary boundary detection information P1 is deactivated when the predetermined first condition is satisfied, that is, becomes a first logic state (logical low state), If the first predetermined condition is not satisfied, the second logic state is activated from the first logic state to the second logic state (logical high state).

In Equation 6, 0.3 to 0.35 is appropriate, and the secondary boundary detection information P is deactivated when the predetermined second condition is satisfied, that is, becomes a first logic state (logical low state). If the predetermined second condition is not satisfied, the second logic state is activated from the first logic state to the second logic state (logical high state).

Accordingly, the symbol clock generator 270 detects the primary boundary detection information P1 when the predetermined first condition is not satisfied, or the secondary boundary detection when the predetermined second condition is not satisfied. As the information P is activated, the first peak position dmax (i-1) is synchronized to the position dmax (i-1) as a boundary between the short training symbol interval and the long training symbol interval in the OFDM standard. It generates and outputs a symbol clock SCLK, which is a clock. The IFFT unit 280 outputs a digital symbol IFTS processed by IFFT by synchronizing the digital signal with the symbol clock SCLK.

When symbol synchronization is performed in this manner, the reason for the improved performance is as follows. First, as a peak value during the initial (approximately t7 interval) 16 samples, when the left side of the ideal peak (sample immediately before the peak) is selected (first case) due to the influence of noise, etc. (the second case) Or the case where the right side (sample immediately after the peak) of the ideal peak is selected (third case), it demonstrates.

In the case of the first case, if the next 16 samples are within a short symbol training interval, as shown in FIG. 6, the probability is still about 80% of the peak value, so that Equation 5 The probability of satisfying the first condition of is large. Since the 17th sample value is the ideal peak position, the probability of satisfying the second condition of Equation 6 is even greater. In addition, in the case of the first case, when the next 16 samples are long symbol training intervals, there is no correlation at all and the probability that the first condition of Equation 5 is satisfied is small. At this time, even if the first condition of Equation 5 is satisfied due to noise, the probability of satisfying the second condition of Equation 6 is much smaller.

In the case of the second case, if the next 16 samples are within a short training symbol interval, the probability of satisfying the first condition of Equation 5 is high as in the first case. In the comparison of the 17 th sample values, that is, the second peaks, the correlation value is relatively large (80% of the ideal peaks), and thus the probability of satisfying the second condition of Equation 6 is high. In the case of the second case, if the next 16 samples are within the long training symbol interval, the same as in the first case.

In the case of the third case, if the next 16 samples are within a short training symbol interval, the first value of Equation 5 is expressed as a relatively high correlation value (80% of the ideal peak) in the comparison of the first peak. 1 Most likely to meet the condition. In the comparison of the 17th sample values, that is, the second peaks, the correlation value is about 50%, which is slightly lower than that of the first case or the second case, but the comparison threshold value, i. As a result, the probability of satisfying the second condition of Equation 6 is relatively high. In the case of the third case, if the next 16 samples are within the long training symbol interval, it is the same as the first case described above.

By comparing the thresholds two times in this way, the peak values are maintained twice in the probability basis of the correlation value when the ideal peak position is not found in the initial 16 sample intervals and correlated with the long training symbol. In the comparison, since the probability of satisfying the thresholds in two times is extremely small, the probability of finding the boundary between the short training symbol interval and the long training symbol interval can be maximized.

FIG. 7 is a graph illustrating synchronization probability when a long training symbol is a reference value of a cross correlation unit in a typical OFDM receiver, and FIG. 8 is a graph illustrating synchronization probability of the OFDM receiver of FIG. 2.

Referring to FIGS. 7 and 8, the symbol synchronization estimation performances of the conventional OFDM receiver and the OFDM receiver of FIG. 2 are shown. In FIG. 8, it is more robust than the frequency offset of FIG. 7, and it can be seen that better performance is obtained even at low SNR.

As described above, the OFDM receiver of the wireless LAN system according to the embodiment of the present invention, by the first-order differential cross correlation unit 230, corresponds to the difference value (DVTS) between the digital signal and the short training symbol of the OFDM standard. Outputs a first-order differential cross correlation value Z1 at a predetermined cross correlation, and a second difference cross correlation unit 240 outputs a difference value between the first differential cross correlation value Z1 and the short training symbol. By outputting the second-order differential cross correlation value Z as the cross correlation with respect to the autocorrelation value ACVTS of the DVTS, the primary peak detector 250 causes the primary peak values Z (dmax * (i-1)). ) And Z (dmax * (i)) are compared to output primary boundary detection information P1 corresponding to the first predetermined condition, and the secondary peak detection unit 260 performs secondary peak values Z (dmax * (i). -1)) and Z (dmax + 1 * (i)) are compared to output the secondary boundary detection information P corresponding to the predetermined second condition. Accordingly, the symbol clock generator 270 selects the first peak position dmax (i-1) as the first boundary detection information P1 or the second boundary detection information P is activated. A symbol clock SCLK, which is a clock synchronized with the position dmax (i-1), is generated by outputting the boundary between the short training symbol interval and the long training symbol interval in the OFDM standard.

As described above, optimal embodiments have been disclosed in the drawings and the specification. Although specific terms have been used herein, they are used only for the purpose of describing the present invention and are not intended to limit the scope of the invention as defined in the claims or the claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, the OFDM receiver of the wireless LAN system according to the present invention performs robust first-order differential cross correlation to a frequency offset by using the difference value of the short training symbol as a reference signal, and performs the difference value (DVTS) of the short training symbol. Based on the autocorrelation value (ACVTS) of the first order cross-correlation, and the correlation value of the first correlation cross correlation Perform symbol synchronization in a short time. Therefore, the response speed of the WLAN system applying the OFDM receiver can be increased.

Claims (16)

An RF module unit for receiving an wireless airwave and extracting and outputting an OFDM analog signal from a signal existing in an assigned channel; An AD converter which samples the OFDM analog signal and converts the OFDM analog signal into a digital signal and outputs the digital signal; A first-order differential cross correlation unit for outputting a first-order differential cross correlation value with a predetermined cross correlation between the digital signal and a difference between short training symbols of an OFDM standard; A second differential cross correlation unit for outputting a second differential cross correlation value as the cross correlation between the predetermined first differential cross correlation value and the auto correlation value of the difference between the short training symbols; In response to the secondary boundary detection information when the initial or predetermined second condition is satisfied, the primary peak value Z (dmax * (i-1), which is the highest peak among the initial or previous 16 sampling values of the secondary differential cross correlation value. )) Is compared with the primary peak value Z (dmax * (i), which is the highest peak among the 16 sampling values from the next position, to output the primary boundary detection information P1 corresponding to the first predetermined condition. A peak detector; In response to the first boundary detection information when the first predetermined condition is satisfied, the second peak value Z (dmax + 1 *) which is the next sampling value after the highest peak value among the previous 16 sampling values of the second differential cross correlation value. (i-1)) in comparison with the second peak value Z (dmax + 1 * (i)), which is the next highest peak value of the sampling values among the 16 sampling values from the next position, the 2 corresponding to the predetermined second condition. A second peak detector for outputting difference boundary detection information; As the primary boundary detection information when the first predetermined condition is not satisfied or the secondary boundary detection information when the predetermined second condition is not satisfied, the primary peak position dmax (i A symbol clock generation unit for generating and outputting a symbol clock which is a clock synchronized with the position dmax (i-1) in view of −1) as a boundary between a short training symbol interval and a long training symbol interval in the OFDM standard; And And an IFFT unit for outputting a digital symbol subjected to IFFT processing by synchronizing the digital signal with the symbol clock. The method of claim 1, wherein the predetermined cross correlation is, Equation representing the digital signal, Where P _k is the k th sample signal, b _k is the ideal k th sample signal in the time domain, T _s is the sample interval, θ ₀ is the initial phase value, N is the point size of the IFFT, and a _n is the nth subchannel. Data symbol on the sender side) And an equation representing a difference value of the short training symbol. Where R1 (k) is the difference between short training symbols By, Where d is the location of the time domain To calculate, the equation representing the predetermined first differential cross-correlation value, (Where Z1 (d) is the first-order differential cross correlation value) OFDM receiver of a WLAN system, characterized in that for calculating. The method according to claim 1, wherein the predetermined first condition is Equation, β * Z (dmax * (i-1)) <Z (dmax * (i)) (Where β is an arbitrary coefficient, Z (dmax * (i-1)) is the initial or previous primary peak, dmax * (i-1) is the position of the initial or previous primary peak, Z (dmax * ( i)) is the current primary peak and dmax * (i) is the current primary peak) OFDM receiver of a wireless LAN system, characterized in that. The method of claim 3, wherein β is OFDM receiver of a wireless LAN system, characterized in that less than 0.5. The method of claim 1, wherein the first boundary detection information, The OFDM receiver of the WLAN system, characterized in that is deactivated when the first predetermined condition is satisfied, and is activated when the first predetermined condition is not satisfied. The method according to claim 1, wherein the predetermined second condition is Equation, γ * Z (dmax + 1 * (i-1)) <Z (dmax + 1 * (i)) Where γ is any coefficient, Z (dmax + 1 * (i-1)) is the initial or previous secondary peak, dmax * (i-1) is the position of the initial or previous secondary peak, Z (dmax * (i)) is the current secondary peak, dmax * (i) is the current secondary peak) OFDM receiver of a wireless LAN system, characterized in that. The method according to claim 6, wherein γ is OFDM receiver of a wireless LAN system, characterized in that less than 0.35. The method of claim 1, wherein the secondary boundary detection information, And deactivated when the predetermined second condition is satisfied, and is activated when the predetermined second condition is not satisfied. Receiving, by the WLAN system, wireless airwaves and extracting and outputting an OFDM analog signal from a signal present in an assigned channel; Sampling, by the wireless LAN system, the OFDM analog signal and converting the digital signal into a digital signal; Outputting, by the wireless LAN system, a first order differential cross correlation value with a predetermined cross correlation of a difference between the digital signal and a short training symbol of an OFDM standard; Outputting, by the wireless LAN system, a second differential cross correlation value as the cross correlation with respect to an autocorrelation value between the predetermined first differential cross correlation value and the difference between the short training symbols; The primary peak Z, which is the highest peak among the initial or previous 16 sampling values of the secondary differential cross correlation value, in response to the secondary boundary detection information when the initial or predetermined second condition is satisfied by the WLAN system. (dmax * (i-1)) is compared with the primary peak value Z (dmax * (i)), which is the highest peak among 16 sampling values from the next position, to obtain the first boundary detection information corresponding to the first predetermined condition. Outputting; By the wireless LAN system, in response to the first boundary detection information when the predetermined first condition is satisfied, a second peak that is a sampling value after the highest peak among the previous 16 sampling values of the second differential cross correlation value; The predetermined value by comparing the value Z (dmax + 1 * (i-1)) with the second peak value Z (dmax + 1 * (i)), which is the next highest peak value of the sampling among the 16 sampling values from the next position. Outputting the secondary boundary detection information corresponding to two conditions; As the wireless LAN system activates the first boundary detection information when the first predetermined condition is not satisfied or the second boundary detection information when the first predetermined condition is not met, the first boundary detection information is activated. Generating and outputting a symbol clock which is a clock synchronized with the position dmax (i-1) by considering the difference peak position dmax (i-1) as a boundary between a short training symbol interval and a long training symbol interval according to the OFDM standard; ; And And outputting, by the wireless LAN system, a digital symbol subjected to IFFT processing by synchronizing the digital signal with the symbol clock. The method of claim 9, wherein the predetermined cross correlation is, Equation representing the digital signal, Where P _k is the k th sample signal, b _k is the ideal k th sample signal in the time domain, T _s is the sample interval, θ ₀ is the initial phase value, N is the point size of the IFFT, and a _n is the nth subchannel. Data symbol on the sender side) And an equation representing a difference value of the short training symbol. Where R1 (k) is the difference between short training symbols By, Where d is the location of the time domain To calculate, the equation representing the predetermined first differential cross-correlation value, (Where Z1 (d) is the first-order differential cross correlation value) OFDM reception method of a wireless LAN system, characterized in that for calculating. The method according to claim 9, wherein the predetermined first condition is Equation, β * Z (dmax * (i-1)) <Z (dmax * (i)) (Where β is an arbitrary coefficient, Z (dmax * (i-1)) is the initial or previous primary peak, dmax * (i-1) is the position of the initial or previous primary peak, Z (dmax * ( i)) is the current primary peak and dmax * (i) is the current primary peak) OFDM reception method of a wireless LAN system, characterized in that. The method of claim 11, wherein β is OFDM reception method of a wireless LAN system, characterized in that less than 0.5. The method of claim 9, wherein the first boundary detection information, And deactivated when the predetermined first condition is satisfied, and is activated when the predetermined first condition is not satisfied. The method according to claim 9, wherein the predetermined second condition is Equation, γ * Z (dmax + 1 * (i-1)) <Z (dmax + 1 * (i)) Where γ is any coefficient, Z (dmax + 1 * (i-1)) is the initial or previous secondary peak, dmax * (i-1) is the position of the initial or previous secondary peak, Z (dmax * (i)) is the current secondary peak, dmax * (i) is the current secondary peak) OFDM reception method of a wireless LAN system, characterized in that. The method according to claim 14, wherein γ is OFDM receiving method of a wireless LAN system, characterized in that less than 0.35. The method of claim 9, wherein the secondary boundary detection information, And deactivated when the second predetermined condition is satisfied, and is activated when the second predetermined condition is not satisfied.